1. Field of the Invention
The present invention relates generally to centrifugal blower assemblies for automotive vehicles. More particularly, the present invention relates to a centrifugal blower assembly having an apparatus for rotating a volume of air entering the assembly.
2. Background Information
Centrifugal blowers and fans generally include an impeller or blower wheel that rotates in a predetermined direction in a housing and which may be driven by an electric motor. The impeller has curved blades which draw air in axially, along the impellers' axis of rotation, and discharge air radially outwardly. Such blowers are used in a variety of applications, such as in heating and cooling systems, especially for automotive applications.
Centrifugal fans have been fitted with well known shutter devices to reduce the opening of the air passage formed through the fan casing to control the capacity of the fan. The shutter arrangement can be closed to provide adequate airflow adjustment while, at the same time, reducing the horsepower requirements of the fan. However, with these type of shutter arrangements, fan pulsations can occur when the air passage opening is partially closed. In those cases where the shutters are opened fully, the incoming air impinging on the impeller blades often results in a substantial amount of boundary layer flow separation due to the angle with which the incoming air contacts the leading edge of the impeller blades. This separation can result in increasing noise, vibration, and harshness as well as degrading the efficiency of the centrifugal blower.
In addition, as the air approaches the blower or fan inlet opening in an axial direction, it tends to reach the middle and lower portions of the blower fan wheel or impeller and flows radially outwardly to the blower housing scroll more from the middle portion of the wheel. Less air blows from the top portion of the impeller and therefore, the fan is inefficient.
To overcome the above-described problems, U.S. Pat. No. 3,781,127 discloses a centrifugal blower which includes a plurality of spin inducing inlet vanes and a mechanism for pivotably supporting the vanes around the outer wall of the inlet to the centrifugal blower. With this arrangement, the capacity or amount of air entering the blower can be controlled and a spin can be imparted to the incoming gas. Alternatively, the vanes can be shut completely, restricting the flow of gas into the blower while imparting a maximum spin to the incoming gas. The system of the '127 patent is attached to a position outside of the housing of the blower.
Each vane of the assembly '127 can pivot to vary the amount of opening to the air entering the fan blower. However, the assembly is costly and complex to manufacture. Furthermore, the assembly needs a mechanism to control the amount of rotation or pivot of each of the blades relative to the blower housing, adding further cost and complexity to the centrifugal blower. Also, the amount of spin imparted by the moveable blades is insufficient to overcome or reduce the boundary layer flow separation around each of the blades of the centrifugal blower. Therefore, it would be advantageous to provide a less expensive and less complicated device which reduces the flow separation around each of the blades of the centrifugal blower impeller, forces incoming air to flow through the entire fan/impeller wheel and improves the efficiency of the blower while reducing the axial force exerted by the gas on the fan hub.